This invention relates, in general, to circuits for converting electrical power, and more particularly, to power factor controllers.
Many types of circuits derive a DC voltage from an AC utility line through a bridge rectifier and a bulk storage capacitor. A rectifying circuit will draw power from the AC utility line when the voltage on the AC utility line exceeds the voltage on the bulk storage capacitor. Power is typically supplied near the utility line peak voltage causing a high charge current spike. The resulting current spikes are extremely nonsinusoidal with a high content of harmonics which results in a poor power factor condition where the input power is much higher than the real power.
A power factor control circuit significantly enhances poor power factor loads by keeping the average AC line current sinusoidal and in phase with the line voltage. A power factor control circuit provides a DC voltage and operates linearly around a nominal or central point of regulation. In general the linear operation is within a narrow range around the regulation point. A power factor control circuit does not respond rapidly when the output is out of regulation by a significant margin. For example, the power factor control circuit will take a significant amount of time to reach the regulation point during initial power up.
Within the narrow range in which the power factor control circuit provides regulation high currents may be provided depending on the loading to the circuit. No load conditions present a regulation problem since a high charging current to the bulk storage capacitor will cause a significant increase in voltage which is generally diverted to the load. No load regulation is normally handled by an overvoltage detection circuit which shuts off drive to the bulk storage capacitor when the output voltage exceeds a predetermined voltage.
It would be of great benefit if a power factor control circuit could be provided that rapidly approaches the regulation point when out of regulation and reduces output voltage variations under no load conditions.